so nothing in this world is comparable. but for the sake of this question, comparison is needed. compare a girl, named Chanie brought up in Monroe, and a girl named Clara brought up in Las vegas, in an extremely progressive neighborhood, where modern orthodox is viewed as fanatic. now lets analyze this chanie and clara. their line of bechira lie in two very diverse places. chanie is faced with challenges such as, having a hard time davening mariv, while clara is struggling with shabbos. however they are both as good or if not better than their upbringing. now, hashem was the one to situate Chanie and Clara in their designated communities. question. wasup with their schar? is it equivalent? their life styles are so nonidentical, but will their oilem haba be corresponding?
It is possible the Clara will have more since
לפום צערא אגרא.
According to the pain is the reward.
לפום צערא אגרא כפי רוב הצער שאתה סובל בלמוד התורה ועשיית המצוה, יהיה שכרך מרובה.
"According to the pain is the reward":According to the greatness of the pain, that you endure in the study of Torah and in the performance of the commandments, will your reward be great.
Ikar tosfois yomtov
וזה בשכר הצער והטורח עצמו, שאם הוא מרובה שכרו מרובה. אבל שכר מצות עצמן אי אתה יודע מתן שכרן. כדתנן בריש פ''ב. ד''ח.
And this is about the reward for the pain and bother itself - that if it is great, its reward will be great. But [regarding] the reward for the [performance of the] commandments themselves, you do not know the gift of their reward, as we learned at the beginning of Chapter 2 -
"Their upbringing" is an excuse only if they do not know the Torah (their obligation)
but if they know there obligation they have to do it,
but their upbringing does effect how hard it is for them and from above we know that acording to the effort is the reward
Quoted in Chafetz Chaim
in Avoth d'R. Nathan: "One time with strain for a hundred times without strain." (That is, the reward for the performance of a mitzvah or the abstention from an issur, which entails strain, is a hundredfold more than for that of the same kind, which entails no strain.)
This is just as Rabbi Dessler in Michtav MaiElliyahu develops the concept of nekudas ha bechirah (point of decision) that each person is rewarded or punished for a decision based on the level that he has reached (as you give in the question). Similarly, the schar of a person is also based on both the effort that he has put in as well as the level that he has reached.
As I explain in more detail at Why did God created physical impulse towards the "wrong" women
Rabbi Eliyahu Dessler in Michtav Me'Eliyahu in Kuntras Habechirah, (Michtav MaEliyahu, Vol. 1, page 111-119) explains that everybody is given free will in order to be able to raise himself to whatever level that he is capable of reaching.
See also Michtav Me'Eliyahu
There is a quip that goes as follows:
What is the reward of the righteous? He will be able to learn in the Bais Medrash of Hashem.
What is the punishment of the wicked? He must learn in the Bais Medrash of Hashem.
This means that while we cannot understand what happens when we reach Olam Haba, we can express it in terms that we understand to be a reward or a punishment. Since each person is different, the what would be reward for one could be a punishment for another. Thus, one cannot state that one reward is "higher" or "better" than the other in the case of the two girls you give in the question. Each one would receive the reward that she is capable of understanding and "enjoying". This is actually something that is based on the level that she manages to reach during her life.